Laser ignition chemical synthesis of bulk Al2O3-TiB2 composites for impact resistance application

The increasing demand for advanced materials has prompted the exploration of energy-efficient processes for near-net shape manufacturing. Laser ignition chemical synthesis (LIChemS) is a novel technology for rapid and cost-effective synthesis of refractory materials. Using a 976 nm quasi-CW diode laser, we manufactured Al2O3-TiB2 composites in situ from aluminum, TiO2, and B2O3. Leveraging low-power laser processing and an exotherm-driven mechanism, which involves keyhole formation, metal vapour ionisation, and Marangoni convection, LIChemS generated plasma for propagating the reaction across the bulk, for laser intensity of 1.13 W/mm2. The adiabatic temperature and activation energy of LIChemS were calculated as 2643 K and 11.6 kJ/mol respectively. A Newtonian cooling model predicted crack generation within the composites for a differential temperature of 349 K between the centre and edges. We propose a new reaction mechanism yielding high-purity composites, displaying only traces of Ti2O3. The composites exhibited skeletal and bulk densities of 4010 kg/m3 (96 %) and 3830 kg/m3 (92 %) respectively, fracture toughness of 5.8 MPa m1/2, and Vickers microhardness of 18.14 ± 0.49 GPa. The optimum Al2O3-TiB2 composite demonstrated 15 % greater compressive strength than monolithic alumina and withstood 174 N before fracturing. An analytical model combining Hertzian contact mechanics with impact mechanics correlated the ball-drop heights during impact testing to the defect sizes within the composites. The composites presented a surface roughness of 14.9 μm and fine dispersion of TiB2 and Ti2O3 nanoparticles within the alumina matrix. The results herein suggest great scalability opportunities for LIChemS in manufacturing customised, high purity, energy demanding materials.